1. Field of the Invention
The present invention relates to an electronic throttle control apparatus adapted to drivingly open and close a throttle valve disposed in an intake passage by means of an actuator in a gasoline engine or a diesel engine.
2. Description of Related Art
There has conventionally been known an electronic throttle control apparatus which is used in a gasoline engine or a diesel engine for a motor vehicle and others. This electronic throttle control apparatus is provided with an electronic throttle including a throttle valve of a linkless type which is disposed in an intake passage in the engine and is drivingly opened and closed by an actuator such as a motor and a controller for controlling the actuator. This controller determines a target opening degree of the electronic throttle (namely, the throttle valve) based on an operated amount of an accelerator pedal operated by a driver. The controller makes feedback control on the actuator by PID control and the like based on a deviation of opening degree between the determined target opening degree and an actual opening degree of the throttle valve detected by a throttle sensor, thereby controlling the electronic throttle so that the actual opening degree approaches the target opening degree.
In the above electronic throttle apparatus, a response and a stable convergence in operations of the electronic throttle often become problems. One of techniques taking those points into consideration is disclosed in Japanese patent unexamined publication No. 10-176579, which is entitled xe2x80x9cThrottle valve control apparatusxe2x80x9d.
In this control apparatus, a controller determines a driving signal (=a control amount) of a throttle valve based on the product obtained by multiplying an opening degree deviation between a requested opening degree (=a target opening) and an actual opening degree of the throttle valve by a control coefficient (=a control gain). The controller has previously stored data on control coefficients (proportional gains and integrating gains) determined according to an opening degree deviation. The data is set such that the smaller the opening degree deviation is, the larger control coefficient is determined. The controller provisionally determines a control coefficient with reference to the above data if the throttle valve opening degree is in a transitional state at the time when the controller receives a signal representing an opening degree deviation. The controller then compares the provisionally determined value of control coefficient with a control coefficient value used in a previous cycle to select a smaller one. The controller calculates a value of a driving signal by multiplying the opening degree deviation by the selected control coefficient. The controller controls the motor based on the calculated value of the driving signal to drivingly open and close the throttle valve.
The above control is explained in detail with reference to a flowchart in FIG. 11. The controller first calculates an opening degree deviation ER between a target opening degree RTA and an actual opening degree VTA in a step 200 and calculates an absolute value (an absolute opening degree deviation) AER of the opening degree deviation ER in a step 201.
In a step 202, the controller determines whether or not the absolute opening degree deviation AER is smaller than a predetermined value A1. If an affirmative decision is made in the step 202, the controller determines that the throttle opening degree is in a steady state and, in a step 220, sets a gain KPb for a steady operation as a final proportional gain KP. In a step 221, the controller sets a gain KIb for the steady operation as a final integrating gain KI and advances the flow to a step 209.
If a negative decision is made in the step 202, on the contrary, the controller determines that the throttle opening degree is in a transitional state and, in the step 203, calculates a proportional gain tKP from the absolute opening degree deviation AER by referring to a proportional gain map (Map 1). In a step 204, the controller calculates an integrating gain tKI from the absolute opening degree deviation AER by referring to an integrating gain map (Map 2). These proportional gain tKP of the proportional gain map and the integrating gain tKI of the integrating gain map have both been set to become smaller as the absolute opening degree deviation AER becomes larger.
In a step 205, the controller then determines whether or not the proportional gain tKP calculated at this time is larger than the final proportional gain KP used at a previous time. If an affirmative decision is obtained in the step 205, the controller advances the flow directly to a step 207. If a negative decision is obtained, on the contrary, the controller updates the final proportional gain KP by the proportional gain tKP calculated at this time and then advances the flow to the step 207. More specifically, since this-time absolute opening degree deviation AER is larger than the previous absolute opening degree deviation AER, the proportional gain tKP which is smaller than the previous final proportional gain KP is selected as this-time final proportional gain KP. This is referred to as xe2x80x9cminimum selectxe2x80x9d.
In a step 207 following the step 205 or 206, the controller determines whether or not the integrating gain tKI calculated at this time is larger than the final integrating gain KI used at a previous time. If an affirmative decision is made, the controller advances the flow directly to a step 209. If a negative decision is made in a step 208, the controller updates the final integrating gain KI by the integrating gain tKI calculated at this time and then advances the flow to the step 209. More specifically, since this-time absolute opening degree deviation AER is larger than the previous absolute opening degree deviation AER, the integrating gain tKI which is smaller than the previous final integrating gain KI is selected as this-time final integrating gain KI. In other words, the xe2x80x9cminimum selectxe2x80x9d is conducted.
In the step 209 following the step 207, 208, or 221, the controller calculates a proportional term VP by multiplying this-time final proportional gain KP by the opening degree deviation ER obtained at this time. In a step 210, the controller calculates an integral term VI by adding the product of this-time final integrating gain KI and this-time opening degree deviation ER to an addition result accumulated up to the previous time. In a step 211, the controller furthermore calculates a PI control amount (controlled variable) VPI by adding the proportional term VP calculated at this time and the integral term VI. In a step 212, the controller converts the PI control amount VPI calculated at this time to a duty ratio DUTY by using a predetermined function expression.
In a step 213, the controller then controls the motor based on the converted duty ratio DUTY to drivingly open and close the throttle valve.
The feature of the above routine is in determination of the final proportional gain KP and the final integrating gain KI by way of the xe2x80x9cminimum selectsxe2x80x9d. This can be shown by a block diagram in FIG. 12. In a block B1, the controller first calculates the opening degree deviation between the target opening degree and the actual opening degree. In a block B2, the controller calculates the control gain according to the opening degree deviation. In a block B3, the controller executes the minimum select to select a smaller one of the calculated control gains. In a block B4, then, the controller determines the control gain obtained by the minimum select as the final control gain.
More specifically, the conventional throttle valve control apparatus has stored the proportional gain tKP and the integrating gain tKI corresponding to the absolute opening degree deviation AER in the form of map. However, even if the absolute opening degree deviation AER is reduced by the motion of the throttle valve, the final proportional gain KP and the final integrating gain KI are not changed when the absolute opening degree deviation AER changes to a smaller value. This makes it possible to achieve high levels of both a response as the absolute opening degree deviation AER is small and a stable convergence as the absolute opening degree deviation AER is large, so that the throttle valve is appropriately driven regardless of operational status.
In the conventional throttle valve control apparatus, however, the response characteristics of the control apparatus may vary delicately by a product variance, a deterioration with age, or a change in temperature condition during operation, etc. Consequently, under such circumstances that the throttle valve temporarily slows down or stops during motion, the final proportional gain KP and the final integrating gain KI are maintained as small values by the minimum select. As a result, it would take much time to converge subsequent motion, which may cause a deterioration in convergence (response).
In other words, the minimum select is performed in the conventional throttle valve control apparatus, so that the final proportional gain KP and the final integrating gain KI remain unchanged when the absolute opening degree deviation AER is in a larger value range, even if the absolute opening degree deviation AER is changed to a smaller value in the range. Accordingly, the proportional term VP and the integral term VI remain unchanged and also the PI control amount VPI and the duty ratio DUTY remain unchanged. The throttle valve is thus slow in motion as before and therefore the convergence (response) of the subsequent motion could not be improved.
This can be explained based on for example the influence of changes in temperature condition around the engine during operation with respect to the characteristics of the motor which drives the throttle valve. FIG. 13 is a graph showing the magnetic property to temperature of a magnet constituting the motor. FIGS. 14 to 16 are graphs showing the motor torque property at 25xc2x0 C., at 120xc2x0 C., and xe2x88x9230xc2x0 C., respectively. In these graphs of the motor torque property, xe2x80x9cT-Nxe2x80x9d indicates a relation between torque and revolution speed and xe2x80x9cT-Ixe2x80x9d indicates a relation between torque and electric current.
As apparent in the graph in FIG. 13, the magnetic flux density of the magnet is reduced as the temperature rises. Comparing the motor torque property at xe2x88x9230xc2x0 C. shown in FIG. 16 with that at 25xc2x0 C. shown in FIG. 14, it is found that electric current and produced torque increase at xe2x88x9230xc2x0 C. Thus, with respect to the control amount applied to the motor, current and torque increase, enhancing a response. Comparing the motor torque property at 120xc2x0 C. shown in FIG. 15 with that at 25xc2x0 C. shown in FIG. 14, on the other hand, it is found that current and produced torque decrease at 120xc2x0 C. Thus, current and torque decrease with respect to the control amount applied to the motor, deteriorating a response.
The above graphs show that when the temperature of the motor excessively rises, the response of the motor would be deteriorated and therefore the motion of the throttle valve becomes slow. This may affect the convergence (response) in subsequent motion of the throttle valve.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide an electronic throttle control apparatus which sets a control gain so that the control gain becomes smaller as a deviation of opening degree between a target opening degree and an actual opening degree becomes larger, and limits a control gain to be set at this time (hereinafter, referred to as xe2x80x9cthis-time control gainxe2x80x9d) by a control gain set at a previous time (hereinafter, referred to as xe2x80x9cprevious control gainxe2x80x9d) at a time when this-time control gain is larger than the previous control gain, wherein a convergence characteristic (a response) of subsequent motion is allowed to be improved even when a motion of a throttle valve slows down in the process.
To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided an electronic throttle control apparatus including: an electronic throttle for drivingly opening and closing a throttle valve by an actuator; target opening degree setting means for setting a target opening degree of the electronic throttle; actual opening degree detection means for detecting an actual opening degree of the electronic throttle; opening degree deviation calculation means for calculating a deviation between the target opening degree and the actual opening degree; control amount calculation means for calculating a control amount of the actuator based on the calculated opening degree deviation and a control gain corresponding to the opening degree deviation; control gain setting means for setting the control gain so that the control gain becomes smaller as the opening degree deviation becomes larger; control gain limitation means for limiting a control gain to be set at this time so as not to change from a control gain set at a previous time when the control gain to be set at this time is larger than the control gain set at a previous time; actuator control means for controlling the actuator based on the calculated control amount; wherein the electronic throttle apparatus including: change speed detection weans for detecting a speed of change of the actual opening degree; and limitation canceling means for canceling the limitation to the control gain by the control gain limitation means when the detected change speed becomes lower than a predetermined value.
In this case, the term xe2x80x9climitationxe2x80x9d by the control gain limitation means indicates applying a guard to the control gain, specifically, maintaining a previously set value of the control gain without substituting it with a value of the control gain to be set at this time.
According to the present invention mentioned above, the opening degree deviation between the target opening degree set by the target opening degree setting means and the actual opening degree detected by the actual opening degree detection means is calculated by the opening degree deviation calculation means. The control gain is set by the control gain setting means so that the control gain becomes smaller as the opening degree deviation becomes larger. Then, the control amount is calculated by the control amount calculation means on the basis of the calculated opening degree deviation and the control gain in correspondence to the opening degree deviation, and the actuator is controlled by the actuator control means on the basis of the control amount. Accordingly, in the case that the opening degree deviation is relatively small, the relatively large control gain is set, whereby the relatively large control amount is calculated. Therefore, the actuator is controlled based on the control amount, whereby the actuator quickly starts operating.
In this case, when the opening degree deviation changes to a smaller value, that is, under a condition that the actual opening degree is approaching the target opening degree, the control gain set according to the change intends to change. However, when the control gain to be set at this time is larger than the control gain set at the previous time, the control gain to be set at this time is limited to the control gain set at the previous time, by means of the control gain limitation means, whereby the change of the control amount is limited. Therefore, the actuator is continuously controlled with keeping the initially calculated control amount, and an excess motion of the actuator is inhibited on a process that the opening degree deviation becomes gradually small.
On the contrary, even in the case that the opening degree deviation changes to the smaller value, when the speed of change of the actual opening degree detected by the change speed detection means becomes lower than the predetermined value due to a temporary slowdown motion of the throttle valve in the process, the limit with respect to the change in the limit gain by the control gain limitation means is cancelled by the limit canceling means. Therefore, the actuator is controlled by the control amount calculated on the basis of the control gain corresponding to the opening degree deviation at that time, in place of the initially calculated control amount, and the motion of the actuator in the middle of the motion becomes quick.
Accordingly, in the electronic throttle control apparatus structured such as to set the control gain so that the control gain becomes smaller as the opening degree deviation between the target opening degree and the actual opening degree becomes larger, calculate the control amount of the actuator on the basis of the control gain and the opening degree deviation, and limit the change in the control gain at a time when the opening degree deviation changed to the smaller value, since the limit with respect to the control gain is cancelled at a time when the change speed of the actual opening degree becomes lower than the predetermined value, it is possible to improve a convergence characteristic (a response) of the subsequent motion even when the motion of the throttle valve slows down in the process.